Question

Explain in brief the formula T=2π√l/g.

Answer 1

$T = 2\pi \sqrt{ \frac{l}{g} } \\ here \\ l - displacement \\ g - acceleration \: due \: to \: gravity$
suppose you have a block and opposite to it there is a cushion and you applied force after that block displaced 'l' before colliding with cushion and then after colliding it came to you.
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so the time period can be conclude from above formula but we have to use acceleration here instead of acceleration due to gravity.

Answer 2

it is the formula of time period where l denotes displacement and g is constant whose value is 9.8.